1. Field of the Invention
The present invention relates to a non-aqueous pigment ink.
2. Description of the Related Art
An inkjet recording system is a printing system in which printing is conducted by spraying a liquid ink with a high degree of fluidity from very fine nozzles, and adhering the ink to a recording medium such as a sheet of paper. These systems enable the printing of high-resolution, high-quality images at high speed and with minimal noise, using a comparatively inexpensive printing apparatus, and are rapidly becoming widespread.
Colorants for the inks used in these inkjet recording systems can be broadly classified into those that use pigments and those that use dyes. Of these, there is a growing tendency for the use of inks that use pigments as the colorants, as such inks exhibit the excellent levels of light resistance, weather resistance and water resistance that are required for high image quality printing.
In terms of the solvent, inks can be broadly classified into aqueous inks and non-aqueous inks. In aqueous inks, a water-based solvent or water is used as the ink medium, and therefore it can sometimes be difficult to disperse the pigment finely within this medium, and then ensure favorable stability of the dispersion.
For this reason, Patent Document 1 proposes an aqueous pigment ink in which the pigment is encapsulated to enable dispersion within the aqueous medium.
However, because the ink is aqueous, the problem of poor water resistance remains.
In contrast, non-aqueous inks that do not use water as the ink solvent, including solvent-based inks that use a volatile solvent as the main constituent and oil-based inks that use a non-volatile solvent as the main constituent, are attracting much attention. Compared with aqueous inks, non-aqueous inks exhibit more favorable drying properties and produce minimal curling of the printed paper, and therefore display excellent printability.
These non-aqueous inks contain a non-aqueous solvent, a pigment and a pigment dispersant and the like. Compared with aqueous inks, non-aqueous inks exhibit superior affinity between the colorant and the solvent, and therefore when the ink is adhered to the paper, a problem arises in that the colorant is not retained on the surface of the paper, but rather penetrates into the interior of the paper together with the solvent, causing a reduction in the ink density at the printed surface (upper surface) of the printed item, and the occurrence of show-through on the non-printed surface (rear surface).
For this reason, in order to improve the print density, Patent Document 2 proposes an ink comprising a pigment complex composed of a pigment, a dispersant and an amine compound.
However, in Patent Document 2, the molecular weight of the resin component that coats the pigment is comparatively small, and the fixability of the ink to the recording medium, and in particular the abrasion resistance on smooth papers, is not entirely satisfactory.    [Patent Document 1] JP 09-151342 A    [Patent Document 2] JP 2008-231364 A
An object of the present invention is to provide a non-aqueous pigment ink that exhibits improved fixability of the ink to recording media and low ink viscosity.